1. Field of the Invention
The present invention relates to a device and a method for manufacturing an engine block, wherein cylinder liners are integrated into the casting mold for bonding the cylinder liners to the cast material and wherein the cylinder liners are secured in a seat having seat surfaces engaging the cylinder liner ends.
2. Description of the Related Art
The aforementioned casting mold is thus formed in part by the cylinder liners delimiting the hollow space of the casting mold. After solidification of the cast material, the cylinder liners are embedded in the engine block and are detached from the mold parts upon removal of the engine block. In order to prevent the cast material form cooling too fast during casting when coming into contact with the cylinder liners and to prevent the resulting incomplete bonding of the cylinder liners within the engine block, the cylinder liners are pre-heated, preferably inductively. During this pre-heating, and to a reduced extent later during casting, the cylinder liners expand causing an undesirable movability of the cylinder liners in their seats. This may cause the cylinder liners to become positioned in the engine block in a position that differs from the desired one. This movability may entail undesirable parallel movement of the cylinder liners as well as slanting of the cylinder axis.
Therefore, it is the primary object of the present invention to provide a new casting mold and casting method of the aforementioned kind with which the manufacture of engine blocks is possible with greater precision than with casting molds and casting methods of the prior art.
In accordance with the present invention, at least one of the seat surfaces is conical and has an incline angle relative to the cross-sectional plane of the cylinder liners such that the ends of the cylinder liner remain in contact with the seat surfaces upon heat expansion of the cylinder liners during casting preparation and during casting.
Preferably, the seat surfaces are conical and have an incline angle xcex11 or xcex12 relative to the cross-sectional plane of the cylinder liner, and the condition tan xcex11+tan xcex12=l/r is fulfilled, wherein l is the axial liner length between points of attack at the seat surfaces and r indicates the corresponding radius.
The invention ensures that during heat expansion, independent of the expansion state, the cylinder liner at all times rests with its ends against the conical seat surfaces so that centering of the cylinder liners is ensured in addition to a sealing action being provided with respect to liquid cast material. The cylinder liner axis can neither be moved in parallel nor can it become inclined. After cooling and solidification of the cast material, the cylinder liners are now embedded precisely in the desired arrangement within the engine block.
In a further embodiment of the invention the angles xcex11 and xcex12 are identical and correspond to the angle xcex1 so that tan xcex1=l/d, wherein d=2r corresponds to the diameter of the liner at the length l. For a cylinder liner with conical end surfaces, the equations tan xcex11+tan xcex12=l/r and tan xcex1=l/d must be fulfilled for each radius r from the inner to the outer radius of the cylinder liner and its corresponding length l. While in the embodiment with different angles xcex11 and xcex12 an axial displacement of the center of gravity of the cylinder liner results during heat expansion, no such displacement occurs when the angles xcex11 and xcex12 are identical.
In a preferred embodiment, the cylinder liners have conical end surfaces which are slanted to match the seat surfaces. Advantageously, such matching seat surfaces and cylinder liner end surfaces provide improved guiding for the centering action. Since the matching surfaces glide relatively easily on one another, the casting mold cannot be damaged during the casting process by the heat expansion of the cylinder liners.
In a further advantageous embodiment of the invention the end surfaces can project past the seat surfaces so that a respective annular undercut is formed which can be filled by the cast material and which realizes an especially stable embedding of the cylinder liner in the cast material.
Preferably, the cast material for the engine block is aluminum or an aluminum alloy and the material for the cylinder liner is gray cast iron, aluminum, or an aluminum alloy.
The cylinder liners can be provided at their exterior with profilings so that axial movement and rotational movement are made more difficult. The cylinder liners are thus especially securely embedded in the cast material.
For realizing a fixed connection of the cylinder liners to the cast material, it is also possible to provide the exterior of the cylinder liners with a coating which produces a metallic connection between the cylinder liners and the cast material. Such a coating can be, for example, AlSi5, AlSi9, or Zn.